1. Field of the Invention
The present invention relates to a photographic film. More particularly, the present invention relates to a photographic film, which can be easily broken to avoid excessive force on the film and film transport devices.
2. Description of the Related Art
It has been general that photographic film in roll form, for example motion picture film, includes a base material formed from modified cellulose, an example of which is cellulose triacetate (TAC) having a high transparency. The base material requires sufficient tensile strength to avoid breakage in the course of photography, development and projection. In the photo film with the TAC base material, the base material must have a thickness of 150 .mu.m or more to have sufficient tensile strength. This required thickness is in turn a drawback of the photo film because it is inevitable that the roll into which the thick photo film is wound has a great diameter, and is highly voluminous when the photo film is of a considerable length.
In view of this drawback, base material for film has been constructed of high tensile polyester, such as polyethylene terephthalate (PET), having sufficient tensile strength even at a thickness of 100 .mu.m. The great tensile strength however makes it difficult to cut the film. If an accident occurs in a transport mechanism of a photo film processor, a motion picture projector, or another optical instrument where the photo film is transported. It is likely that excessive tensile force is applied to the photo film, and transmitted to the transport mechanism, of which roller shafts are deformed and damaged. The photo film is also likely to be deformed by the excessive tensile force. If a long portion of the photo film is damaged. The image and sound on this portion are last.
To overcome the shortcomings of such high tensile photo film, JP-A 6-11794 discloses an improvement in film. In this film, an auxiliary hole is formed between adjacent perforations in a rectangular or triangular shape. The auxiliary hole has a sharp corner, which, upon application of an excessive force, starts being torn, to induce breakage of the photo film in its width direction. This protects the roller shafts of handling device from deformation, and protects the photo film from stretching.
It is general for the motion picture photo film to have a sound track and/or a recording area of sound data; the sound track disposed beside the train of perforations and extended in the length direction of the photo film and the sound data recording area disposed between adjacent perforations. In the high tensile photo film, the auxiliary hole of JP-A 6-11794 is inevitably located in the sound track and/or the sound data recording area, to cut off part of the sound information. It is not practical to change the position of the sound track, because a motion picture projector would have to be redesigned for the changed position of the sound track. Also, forming the auxiliary hole in addition to the perforations raises the manufacturing cost of the photo film.